With the implementation of the concept of "Energy Internet", the integrated energy system as the physical carrier of the Energy Internet has been further developed. A regional integrated energy system optimal operation model considering flexible heating load is proposed. Firstly, combined with the basic principles and operation characteristics of typical equipment in the integrated energy system, the main equipment model of the integrated energy system is formed. Based on the user's work and rest rules, a flexible heating load model considering the user's flexible comfort constraints is constructed to increase the system's operation flexibility. Then, a mathematical model for the optimal operation of the regional integrated energy system based on the bus-based structure is constructed. Finally, three different heat and power dispatch methods are defined to analyze the benefits of the combined heat and power dispatch in an integrated energy system. The simulation results show that the optimal operation model of regional integrated energy system considering flexible heating load can improve energy efficiency and reduce the system operation cost.